JP-2009-57924A shows that an injection time delay “td” is defined as the control parameter. The injection time delay “td” represents a time period from when a fuel injection command is generated toward a fuel injector until when a fuel is actually injected into a cylinder of an internal combustion engine. A fuel pressure sensor provided to the fuel injector detects a time point at which the fuel pressure starts to decrease due to a fuel injection, whereby the injection time delay “td” is measured. This measured injection time delay “td” is successively learned and an output timing of the fuel injection command is controlled based on the learned time delay “td”.
The injection time delay “td” depends on a fuel pressure supplied to the fuel injector at the time of fuel injection. According to the present inventor's study, the injection time delay “td” (control parameter) is learned in association with the fuel pressure (variable)
That is, as shown in FIG. 12A, the injection time delay td(30), td(50), td(80) is successively updated as a learning value with respect to the fuel pressure 30 Mpa, 50 MPa, 80 Mpa. For example, in a case that the measured time delay is indicated by a point “AO” in FIG. 12A, the learning value td(50) which is most close to the point “AO” is updated by interpolation. Specifically, an intersection between a straight line “L” connecting the learning value td(30) and the measured point “AO” and a vertical line representing the fuel pressure 50 MPa is learned as the learning value td(50).
In a case that the relationship between the fuel pressure and the time delay “td” is indicated by a curved line “R” in FIG. 12B and the measured points “A1”, “A2”, and “A3” are repeatedly measured on the curved line “R”, the learning value td(50) is successively updated to the value “B1”, “B2”, “B3”. That is, the learning value td(50) repeatedly increases and decreases, which may cause a hunting.
JP-2011-1916A published on Jan. 6, 2011, which corresponds to US-2010-0324702A1 published on Dec. 23, 2010, shows a learning device in which the time delay “td” and the fuel pressure are stored as vector values and a measurement vector consisting of measured values of the time delay “td” and the fuel pressure are computed. Then, a stored learning vector is updated based on the measurement vector. Thereby, it can be restricted that the updated learning vector causes a hunting.
In a case that multiple variables (for example, fuel pressure and fuel injection quantity) are correlated with a control parameter (time delay “td”), the learning map is a three-dimensional map. In such a three-dimensional map, when the control parameter corresponding to a current variable is computed by interpolating the learning vectors, it is likely that following problems may occur.
That is, in an initial stage of learning, it is likely that the stored learning value may deviate from an actual value because the stored learning value is an initial value. In a case that successive learning values are a newest learning value and an initial value, these values significantly deviate from each other. This tendency appears on a vector map.
For example, in a case of maps (usual map) shown in FIGS. 12A and 12B, when updating the learning value td(50), the learning value td(50) is updated based on the adjacent learning value td(30) and the measured point “AO”. Meanwhile, in a case of a vector map, the learning vector is updated irrespective of the adjacent learning values, which causes a significant deviation between adjacent learning values.
In a three-dimensional vector map, when an intersection between a surface including multiple (four or more) learning vectors and current variables (fuel pressure and fuel injection quantity) is computed as a control parameter (time delay “td”) by interpolating, since the adjacent learning vectors significantly deviate from each other, the surface for interpolation becomes a skew surface greatly twisted. Thus, a complicated interpolation by spline is necessary, whereby an interpolation processing load becomes huge.
It should be noted that the dates of publication of the above JP-2011-1916A and US-2010-0324702A1 are later than a priority date (Dec. 10, 2010) of the present application.